A centerline is an imaginary vertical plane that is perpendicular to the length of the datum plane through the center of the vehicle. The centerline is any line drawn through the center of the vehicle's datum. The symbol for centerline is CL.

Centerline length measurements are 3 dimensional measurements. The 3 dimensions are the following:

1. Length, the distance between 2 points when the height is parallel to the center plane.
2. Height, the measurement is parallel to the datum plane.
3. Width, the measurement is parallel to the center plane.

Show the horizontal width and length dimensions of the underbody from the bottom of the underbody. Show the vertical dimensions from the side of the underbody. Use the datum plane as a base for all vertical, height, measurements.